Elephant is an object database for Common Lisp. It supports
storing CLOS objects and most lisp primitives, and access to
BTrees. It uses Sleepycat / Berkeley DB, a widely-distributed
embedded database; many unix systems have it installed by default.
Sleepycat is server-less, ACID compliant, transactional, process and
thread safe, and fast relative to relational databases; hopefully
Elephant inherits these properties.

Version 0.9.0 is now released. ASDF install should work but problems have been reported against it.

Version 0.9.1+ will have support for a back-end repository using Postmodern which is about twice as fast the the generic CL-SQL backend.

Elephant has an extensive manual written by Ian Eslick, who has done most of the recent developement.